In the prior art, submarine cables within offshore wind power installations between individual wind power plants are laid by means of so-called “cable-laying ships” on and/or in the seabed as infield submarine cable of lesser diameter, or from offshore wind power installations to the mainland as export submarine cables of larger diameter.
A submarine cable of this type, which in the radial cross section is cylindrical, for the transmission of three-phase current or high-voltage DC (HVDC) in the prior art is composed of a plurality of power conductors, in particular from copper, and/or of a plurality of data conductors, in particular from copper or glass fibers or man-made fibers, which are received in a tubular cable protection sheath (jacketing) in particular from flexible plastics or metal, and there are embedded in a watertight manner and protected against mechanical and chemical damage.
The layers of the tubular cable protection sheath, from radially outboard to radially inboard, may be configured as follows: Polyethylene tube (PET), biaxially oriented polyester film (boPET), twisted steel ropes as a tubular armor, aluminum tube as a water barrier, polycarbonate tube, copper or aluminum tube, Vaseline.
An alternative construction of the layers of the tubular cable protection sheath may be configured as follows: polypropylene ropes (PP) bitumen layer, armor, bitumen layer, embedding layer.
Of course, further constructions of the layers of the tubular cable protection sheath may also be possible, said further constructions are all to be comprised by the present invention.
The power and data conductors of the submarine cable, lie so as to be embedded in a protective manner by a casting and/or dipping procedure, for example, within the Vaseline layer or the embedding layer, respectively.
The disadvantage is that conventional offshore submarine cables due to their armor which in comparison with onshore cables is very complex have a greater weight, a larger external diameter, greater wall thicknesses, and a larger minimum bending radius. Due to more difficult handling, that is to say manufacturing, storing, transporting, and laying on/in the seabed, the offshore submarine cables are thus more cost intensive.
A further significant disadvantage is that in the case of the offshore cables long delivery times as compared with onshore cables have to be taken into account, as there are only a few (presently three) specialized manufacturers thereof.
Further disadvantages are the comparatively high transmission losses due to induction between the power and data conductors and the armor, this in turn requiring a comparatively large cross-sectional area of the conductors, in particular in the case of three-phase current transmission. Thus, connection of the offshore cables within the conversion pieces to other offshore or onshore cables or to transformer stations is also associated with higher costs.